/**
 * Copyright (C) 2002-2015   The FreeCol Team
 * <p>
 * This file is part of FreeCol.
 * <p>
 * FreeCol is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 * <p>
 * FreeCol is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with FreeCol.  If not, see <http://www.gnu.org/licenses/>.
 */

package net.sf.freecol.server.ai.mission;

import java.util.logging.Logger;

import javax.xml.stream.XMLStreamException;

import net.sf.freecol.common.io.FreeColXMLReader;
import net.sf.freecol.common.io.FreeColXMLWriter;
import net.sf.freecol.common.model.Ability;
import net.sf.freecol.common.model.Colony;
import net.sf.freecol.common.model.CombatModel;
import net.sf.freecol.common.model.IndianSettlement;
import net.sf.freecol.common.model.Location;
import net.sf.freecol.common.model.Direction;
import net.sf.freecol.common.model.PathNode;
import net.sf.freecol.common.model.Settlement;
import net.sf.freecol.common.model.Tension;
import net.sf.freecol.common.model.Tile;
import net.sf.freecol.common.model.Unit;
import net.sf.freecol.common.model.pathfinding.CostDeciders;
import net.sf.freecol.common.model.pathfinding.GoalDecider;
import net.sf.freecol.common.util.LogBuilder;
import net.sf.freecol.server.ai.AIMain;
import net.sf.freecol.server.ai.AIMessage;
import net.sf.freecol.server.ai.AIUnit;


/**
 * Mission for attacking a specific target, be it a Unit or a Settlement.
 */
public class UnitSeekAndDestroyMission extends Mission
{

    private static final Logger logger = Logger.getLogger( UnitSeekAndDestroyMission.class.getName( ) );

    /** The tag for this mission. */
    private static final String tag = "AI seek+destroyer";

    /**
     * The object we are trying to destroy. This can be a
     * either <code>Settlement</code> or a <code>Unit</code>.
     */
    private Location target, transportTarget;


    /**
     * Creates a mission for the given <code>AIUnit</code>.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param target The object we are trying to destroy.  This can be
     *     either a <code>Settlement</code> or a <code>Unit</code>.
     */
    public UnitSeekAndDestroyMission( AIMain aiMain, AIUnit aiUnit,
                                      Location target )
    {
        super( aiMain, aiUnit, target );
    }

    /**
     * Creates a new <code>UnitSeekAndDestroyMission</code> and reads
     * the given element.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param xr The input stream containing the XML.
     * @throws XMLStreamException if a problem was encountered
     *      during parsing.
     * @see net.sf.freecol.server.ai.AIObject#readFromXML
     */
    public UnitSeekAndDestroyMission( AIMain aiMain, AIUnit aiUnit,
                                      FreeColXMLReader xr ) throws XMLStreamException
    {
        super( aiMain, aiUnit );

        readFromXML( xr );
    }


    /**
     * Extract a valid target for this mission from a path.
     *
     * @param aiUnit The <code>AIUnit</code> to perform the mission.
     * @param path A <code>PathNode</code> to extract a target from.
     * @return A target for this mission, or null if none found.
     */
    public static Location extractTarget( AIUnit aiUnit, PathNode path )
    {
        final Location loc = ( path == null ) ? null
                : path.getLastNode( ).getLocation( );
        Tile t;
        Unit u;
        return ( loc == null || aiUnit == null || aiUnit.getUnit( ) == null )
                ? null
                : ( invalidReason( aiUnit, loc.getSettlement( ) ) == null )
                ? loc.getSettlement( )
                : ( ( t = loc.getTile( ) ) != null
                && invalidReason( aiUnit,
                                  u = t.getDefendingUnit( aiUnit.getUnit( ) ) ) == null )
                ? u
                : null;
    }

    /**
     * Scores a potential attack on a settlement.
     *
     * Do not cheat and look inside the settlement.
     * Just use visible facts about it.
     *
     * FIXME: if we are the REF and there is a significant Tory
     * population inside, assume traitors have briefed us.
     *
     * @param aiUnit The <code>AIUnit</code> to do the mission.
     * @param path The <code>PathNode</code> to take to the settlement.
     * @param settlement The <code>Settlement</code> to attack.
     * @return A score of the desirability of the mission.
     */
    private static int scoreSettlementPath( AIUnit aiUnit, PathNode path,
                                            Settlement settlement )
    {
        if ( invalidSettlementReason( aiUnit, settlement ) != null )
        {
            return Integer.MIN_VALUE;
        }
        final Unit unit = aiUnit.getUnit( );
        final CombatModel combatModel = unit.getGame( ).getCombatModel( );

        int value = 1020;
        value -= path.getTotalTurns( ) * 100;

        final double off = combatModel.getOffencePower( unit, settlement );
        value += ( int ) Math.round( off * 50 );

        if ( settlement instanceof Colony )
        {
            // Favour high population (more loot:-).
            Colony colony = ( Colony ) settlement;
            value += 50 * colony.getUnitCount( );
            if ( colony.hasStockade( ) )
            { // Avoid fortifications.
                value -= 200 * colony.getStockade( ).getLevel( );
            }
        }
        else if ( settlement instanceof IndianSettlement )
        {
            // Favour the most hostile settlements
            IndianSettlement is = ( IndianSettlement ) settlement;
            Tension tension = is.getAlarm( unit.getOwner( ) );
            if ( tension != null ) value += tension.getValue( ) / 2;
        }
        return aiUnit.getAIOwner( ).adjustMission( aiUnit, path,
                                                   UnitSeekAndDestroyMission.class, value );
    }

    /**
     * Scores a potential attack on a unit.
     *
     * @param aiUnit The <code>AIUnit</code> to do the mission.
     * @param path The <code>PathNode</code> to take to the settlement.
     * @param defender The <code>Unit</code> to attack.
     * @return A score of the desirability of the mission.
     */
    private static int scoreUnitPath( AIUnit aiUnit, PathNode path,
                                      Unit defender )
    {
        if ( invalidUnitReason( aiUnit, defender ) != null )
        {
            return Integer.MIN_VALUE;
        }
        final Unit unit = aiUnit.getUnit( );
        final Tile tile = path.getLastNode( ).getTile( );
        final int turns = path.getTotalTurns( );
        final CombatModel combatModel = unit.getGame( ).getCombatModel( );
        final double off = combatModel.getOffencePower( unit, defender );
        final double def = combatModel.getDefencePower( unit, defender );
        if ( tile == null || off <= 0 ) return Integer.MIN_VALUE;

        int value = 1020 - turns * 100;
        value += 100 * ( off - def );

        // Add a big bonus for treasure trains on the tile.
        // Do not cheat and look at the value.
        value += 1000 * tile.getUnitList( ).stream( )
                .filter( u -> u.canCarryTreasure( ) && u.getTreasureAmount( ) > 0 )
                .count( );

        if ( defender.isNaval( ) )
        {
            if ( tile.isLand( ) ) value += 500; // Easy win
        }
        else
        {
            if ( defender.hasAbility( Ability.EXPERT_SOLDIER )
                    && ! defender.isArmed( ) ) { value += 100; }
        }
        return aiUnit.getAIOwner( ).adjustMission( aiUnit, path,
                                                   UnitSeekAndDestroyMission.class, value );
    }

    /**
     * Evaluate a potential seek and destroy mission for a given unit
     * to a given tile.
     *
     * @param aiUnit The <code>AIUnit</code> to do the mission.
     * @param path A <code>PathNode</code> to take to the target.
     * @return A score for the proposed mission.
     */
    public static int scorePath( AIUnit aiUnit, PathNode path )
    {
        Location loc = extractTarget( aiUnit, path );
        return ( loc instanceof Settlement )
                ? scoreSettlementPath( aiUnit, path, ( Settlement ) loc )
                : ( loc instanceof Unit )
                ? scoreUnitPath( aiUnit, path, ( Unit ) loc )
                : Integer.MIN_VALUE;
    }

    /**
     * Gets a <code>GoalDecider</code> for finding the best colony
     * <code>Tile</code>, optionally falling back to the nearest colony.
     *
     * @param aiUnit The <code>AIUnit</code> that is searching.
     * @param deferOK Not used in this mission.
     * @return A suitable <code>GoalDecider</code>.
     */
    private static GoalDecider getGoalDecider( final AIUnit aiUnit,
                                               boolean deferOK )
    {
        return new GoalDecider( )
        {
            private PathNode bestPath = null;
            private int bestValue = Integer.MIN_VALUE;

            @Override
            public PathNode getGoal( ) { return bestPath; }

            @Override
            public boolean hasSubGoals( ) { return true; }

            @Override
            public boolean check( Unit u, PathNode path )
            {
                int value = scorePath( aiUnit, path );
                if ( bestValue < value )
                {
                    bestValue = value;
                    bestPath = path;
                    return true;
                }
                return false;
            }
        };
    }

    /**
     * Finds a suitable seek-and-destroy target path for an AI unit.
     *
     * @param aiUnit The <code>AIUnit</code> to find a target for.
     * @param range An upper bound on the number of moves.
     * @param deferOK Not implemented in this mission.
     * @return A path to the target, or null if none found.
     */
    public static PathNode findTargetPath( AIUnit aiUnit, int range,
                                           boolean deferOK )
    {
        if ( invalidAIUnitReason( aiUnit ) != null ) return null;
        final Unit unit = aiUnit.getUnit( );
        final Location start = unit.getPathStartLocation( );

        // Can the unit legally reach a valid target from where it
        // currently is?
        return unit.search( start, getGoalDecider( aiUnit, false ),
                            CostDeciders.avoidIllegal( ), range, unit.getCarrier( ) );
    }

    /**
     * Finds a suitable seek-and-destroy target for an AI unit.
     *
     * @param aiUnit The <code>AIUnit</code> to find a target for.
     * @param range An upper bound on the number of moves.
     * @param deferOK Not implemented in this mission.
     * @return A suitable target, or null if none found.
     */
    public static Location findTarget( AIUnit aiUnit, int range,
                                       boolean deferOK )
    {
        PathNode path = findTargetPath( aiUnit, range, deferOK );
        return ( path != null ) ? extractTarget( aiUnit, path )
                : null;
    }

    /**
     * Why would a UnitSeekAndDestroyMission be invalid with the given unit.
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @return A reason why the mission would be invalid, or null if
     *     none found.
     */
    private static String invalidMissionReason( AIUnit aiUnit )
    {
        String reason = invalidAIUnitReason( aiUnit );
        return ( reason != null )
                ? reason
                : ( ! aiUnit.getUnit( ).isOffensiveUnit( ) )
                ? Mission.UNITNOTOFFENSIVE
                : ( aiUnit.getUnit( ).hasAbility( Ability.SPEAK_WITH_CHIEF ) )
                ? "scouts-should-not-seek-and-destroy"
                : null;
    }

    /**
     * Why would a UnitSeekAndDestroyMission be invalid with the given unit
     * and settlement.
     *
     * @param aiUnit The <code>AIUnit</code> to seek-and-destroy with.
     * @param settlement The <code>Settlement</code> to test.
     * @return A reason why the mission would be invalid, or null if
     *     none found.
     */
    private static String invalidSettlementReason( AIUnit aiUnit,
                                                   Settlement settlement )
    {
        String reason = invalidTargetReason( settlement );
        if ( reason != null ) return reason;
        final Unit unit = aiUnit.getUnit( );
        return ( unit.isNaval( ) )
                ? "unit-is-naval"
                : ( settlement.getOwner( ) == unit.getOwner( ) )
                ? Mission.TARGETOWNERSHIP
                : invalidAttackReason( aiUnit, settlement.getOwner( ) );
    }

    /**
     * Why would a UnitSeekAndDestroyMission be invalid with the given unit
     * and target unit.
     *
     * @param aiUnit The <code>AIUnit</code> to seek-and-destroy with.
     * @param unit The target <code>Unit</code> to test.
     * @return A reason why the mission would be invalid, or null if
     *     none found.
     */
    private static String invalidUnitReason( AIUnit aiUnit, Unit unit )
    {
        String reason = invalidTargetReason( unit );
        if ( reason != null ) return reason;
        final Tile tile = unit.getTile( );
        return ( tile == null )
                ? "target-not-on-map"
                : ( aiUnit.getUnit( ).getOwner( ) == unit.getOwner( ) )
                ? Mission.TARGETOWNERSHIP
                : ( tile.hasSettlement( ) )
                ? "target-in-settlement"
                : ( ! aiUnit.getUnit( ).isTileAccessible( tile ) )
                ? "target-incompatible"
                : invalidAttackReason( aiUnit, unit.getOwner( ) );
    }

    /**
     * Why would this mission be invalid with the given AI unit?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @return A reason for mission invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit )
    {
        return invalidMissionReason( aiUnit );
    }

    /**
     * Why would this mission be invalid with the given AI unit and location?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param loc The <code>Location</code> to check.
     * @return A reason for invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit, Location loc )
    {
        String reason = invalidMissionReason( aiUnit );
        return ( reason != null )
                ? reason
                : ( loc instanceof Settlement )
                ? invalidSettlementReason( aiUnit, ( Settlement ) loc )
                : ( loc instanceof Unit )
                ? invalidUnitReason( aiUnit, ( Unit ) loc )
                : Mission.TARGETINVALID;
    }


    // Implement Mission
    //   Inherit dispose, isOneTime

    /**
     * {@inheritDoc}
     */
    @Override
    public int getBaseTransportPriority( )
    {
        return NORMAL_TRANSPORT_PRIORITY - 5;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location getTransportDestination( )
    {
        if ( ! isValid( ) ) return null;
        Location loc = ( transportTarget != null ) ? transportTarget : target;
        return ( getUnit( ).shouldTakeTransportTo( loc ) ) ? loc : null;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location getTarget( )
    {
        return target;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setTarget( Location target )
    {
        if ( target == null
                || target instanceof Unit || target instanceof Settlement )
        {
            this.target = target;
            Unit unit = getUnit( );
            transportTarget = null;
            if ( unit.shouldTakeTransportTo( target )
                    && ( target instanceof Settlement ) )
            {
                Settlement settlement = ( Settlement ) target;
                if ( settlement.isConnectedPort( ) )
                {
                    transportTarget = settlement.getTile( )
                            .getBestDisembarkTile( unit.getOwner( ) );
                    logger.finest( tag + " chose dropoff " + transportTarget
                                           + " for attack on "
                                           + ( ( settlement.canBombardEnemyShip( ) ) ? "hazardous"
                            : "normal" )
                                           + " settlement " + settlement.getName( )
                                           + ": " + this );
                }
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location findTarget( )
    {
        return findTarget( getAIUnit( ), 4, false );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String invalidReason( )
    {
        return invalidReason( getAIUnit( ), getTarget( ) );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Mission doMission( LogBuilder lb )
    {
        lb.add( tag );
        final AIUnit aiUnit = getAIUnit( );
        String reason = invalidReason( );
        if ( isTargetReason( reason ) )
        {
            Colony colony;
            Mission m;
            if ( Mission.TARGETOWNERSHIP.equals( reason )
                    && getTarget( ) instanceof Colony
                    && ( colony = ( Colony ) getTarget( ) ) != null
                    && getPlayer( ).owns( colony )
                    && ( m = getAIPlayer( ).getDefendSettlementMission( aiUnit,
                                                                        colony ) ) != null )
            {
                return lbDone( lb, true, " capturing colony ", colony.getName( ) );
            }
            return retargetMission( reason, lb );
        }
        else if ( reason != null )
        {
            return lbFail( lb, false, reason );
        }

        // Is there a target-of-opportunity?
        final Unit unit = getUnit( );
        Location nearbyTarget = ( unit.isOnCarrier( ) ) ? null
                : findTarget( aiUnit, 1, false );
        if ( nearbyTarget != null )
        {
            if ( getTarget( ) == null )
            {
                setTarget( nearbyTarget );
                return lbRetarget( lb );
            }
            if ( nearbyTarget == getTarget( ) )
            {
                nearbyTarget = null;
            }
            else
            {
                Tile now = unit.getTile( );
                Tile nearbyTile = nearbyTarget.getTile( );
                Tile targetTile = getTarget( ).getTile( );
                if ( now != null && nearbyTile != null && targetTile != null
                        && ( now.getDistanceTo( nearbyTile )
                        >= now.getDistanceTo( targetTile ) ) )
                {
                    nearbyTarget = null;
                }
                else
                {
                    lb.add( ", found target of opportunity ", nearbyTarget );
                }
            }
        }

        // Go to the target.
        Location currentTarget = ( nearbyTarget != null ) ? nearbyTarget
                : getTarget( );
        // Note avoiding other targets by choice of cost decider.
        Unit.MoveType mt = travelToTarget( currentTarget,
                                           CostDeciders.avoidSettlementsAndBlockingUnits( ), lb );
        switch ( mt )
        {
            case MOVE_HIGH_SEAS:
            case MOVE_NO_MOVES:
            case MOVE_NO_REPAIR:
            case MOVE_ILLEGAL:
                return lbWait( lb );

            case MOVE_NO_ACCESS_EMBARK:
            case MOVE_NO_TILE:
                return this;

            case ATTACK_UNIT:
            case ATTACK_SETTLEMENT:
                Tile unitTile = unit.getTile( );
                Settlement settlement = unitTile.getSettlement( );
                if ( settlement != null && settlement.getUnitCount( ) < 2 )
                {
                    // Do not risk attacking out of a settlement that
                    // might collapse.  Defend instead.
                    Mission m = getAIPlayer( )
                            .getDefendSettlementMission( aiUnit, settlement );
                    return lbDone( lb, m != null, " desperate defence of ",
                                   settlement );
                }
                Direction d = unitTile.getDirection( currentTarget.getTile( ) );
                assert d != null;
                AIMessage.askAttack( aiUnit, d );
                return lbAttack( lb, currentTarget );

            default:
                return lbMove( lb, mt );
        }
    }


    // Serialization

    private static final String TARGET_TAG = "target";


    /**
     * {@inheritDoc}
     */
    @Override
    protected void writeAttributes( FreeColXMLWriter xw ) throws XMLStreamException
    {
        super.writeAttributes( xw );

        if ( target != null )
        {
            xw.writeAttribute( TARGET_TAG, target.getId( ) );
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void readAttributes( FreeColXMLReader xr ) throws XMLStreamException
    {
        super.readAttributes( xr );

        target = xr.getLocationAttribute( getGame( ), TARGET_TAG, false );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String getXMLTagName( ) { return getXMLElementTagName( ); }

    /**
     * Gets the tag name of the root element representing this object.
     *
     * @return "unitSeekAndDestroyMission".
     */
    public static String getXMLElementTagName( )
    {
        return "unitSeekAndDestroyMission";
    }
}
